Among recording and reproducing devices with erasable type optical disks possessing commutability (portability), there are units in which an error map can be written on an individual optical disk. Written within this error map is control data for identifying defective sector and track data, for example, and for writing data to alternate locations when defective sectors/tracks exist. A recording and reproducing device like this is structured so that an error map is read into a RAM located in the unit where the optical disk is inserted. In this manner, an error map access is performed on the optical disk. As a consequence, when a host device and host program access an optical disk via this recording and reproducing device, even if accessing a defective sector, this will not cause problems to the host device because processing automatically shifts to an alternate sector or the like. When a new defective sector is discovered during accessing, or when it becomes necessary to perform new alternate processing, this recording and reproducing device erases and updates the error map.
In conventional optical recording medium recording and reproducing device, the aforementioned error map has been recorded at one specific location on the optical disk.
Now, when rewriting recorded data in an optical modulation type magneto-optical disk recording and reproducing device, it is necessary to erase the area first. Because of this, when an error map is updated in conventional recording and reproducing devices, it is also necessary to record the new error map after erasing the prior error map, which was recorded in the record area of the error map.
Therefore, after erasing the prior error map and before recording the new error map, if for some unexpected reason electric power to the device fails, all contents of the error map will be lost. Such problems have occurred.
If the content of the error map is lost, this may offer no problems concerning defective sectors or tracks, but it is extremely difficult to recover alternate data, and may be impossible to read data recorded at an alternate location.
Even with magnetic modulation type magneto-optical disks, or in phase transition type optical disk recording and reproducing devices, if electric power fails during error map erase processing, possibly the same problem can occur.